Reference is a category for sites devoted to the study of and access to information itself - teaching it (Education), using it (Knowledge Management), storing it (Libraries, Museums) - or sites containing information on topics varied and comprehensive enough that they could not be classified under the other top level Open Directory categories (Dictionaries, Directories, Encyclopedias).
Online calculators are used to perform either simple or complex mathematical operations. These can be accessed online without having to download. They quite often use either JavaScript or Java code.
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